1. Field of the Invention
The present invention relates to an image forming apparatus which can form an image on a long sheet.
2. Description of Related Art
Conventionally, image forming apparatuses (such as a printer, a copier, and a facsimile machine) which can form an image on a long sheet such as a roll sheet and a continuous sheet (continuous form paper) are known. For example, an electrophotographic image forming apparatus is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing at a fixing section, whereby an image is formed on the sheet.
In the case where an image is formed on a long sheet in such an image forming apparatus, if the long sheet is kept tightly sandwiched by a fixing nip during warming-up prior to the start of image formation or during cooling-down after image formation, discoloration (burn) or deformation of the long sheet is caused due to the heat directly applied to the long sheet. Therefore, normally, in a non-image formation period during which image formation is not performed, a fixing side member (for example, a fixing roller) and a back side supporting member (for example, a pressure roller) that form a fixing nip are separated from each other (see, for example, Japanese Patent Application Laid-Open No. 2008-233770).
In addition, discoloration or deformation of a long sheet may be prevented by conveying the long sheet when, like at the time of the warming-up or the cooling-down, the fixing temperature (the temperature of a region near the fixing side member) is higher than a given temperature (a temperature that does not cause discoloration or deformation of the long sheet) but image formation is not performed.
However, in the technique in which a long sheet is kept conveyed during the warming-up and the cooling-down, the long sheet is wastefully consumed without being noticed by the user. This may make the user feel that the long sheet is consumed more than expected, and the user may become distrustful. In addition, this technique cannot be said to be favorable for the user who wants to save the consumption amount of the long sheet.